Amino acids, essential to animal and human nutrition are important as food additives, feed supplements, artificial sweeteners, and intravenous solutions; thus production and purification of amino acids is an important procedure. Descriptively, amino acids are organic acids containing an amino group. These compounds can be obtained by hydrolysis of a protein, by organic synthesis, or by fermentation. As a general rule, all naturally occurring amino acids are alpha-amino acids, having the --NH.sub.2 group attached to the carbon atom next to the COOH group, beta-alanine being an exception to this generalization. Some amino acids are termed essential meaning that they are required for an organism's growth, but can not be synthesized by its body. Essential amino acids for human beings are: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Due to present industrial procedures it is necessary to remove amino acids from dilute fermentation broths and other aqueous mixtures. Current methods used to remove and purify amino acids are crystallization, chromatography, ion-exchange, and extraction. One such method, described in U.S. Patent No. 2,894,954 teaches that amino acids can be removed as a solute in N-hexylamine by a plurality of liquid/liquid contacting zones. In accordance with this method the N-hexylamine is then separated from the amino acids.
Another extraction method used to separate amino acids from fermentation broths and other aqueous mixtures is discussed in: "Quantitative determinations by ion pair extraction", ACLA PHARM. SNEC. 12, 407-416 (1975), by Thomas Nordgren, and Rolf Modine which teaches the extraction of amino acids from fermentation broths by combining a water soluble extractant, tetrapentylammoniumiodide with an aqueous phase containing amino acids, and subsequently washing with methylene chloride. This method, disadvantageously has a tendency to leave water soluble ion pairs formed by the combination of extractant and amino acid in the aqueous phase, which are not extracted in the organic phase.
Another problem encountered in the purification of amino acids is how to deal with the large amounts of water involved. The problem becomes more acute when the aqueous solution is very dilute. The process of the instant invention provides an effective method of extracting amino acids from such dilute solutions. It is also an object of the instant invention to provide a process for extracting amino acids from fermentation broths and other aqueous mixtures which also, advantageously, works well at pH extremes. Other objects will become apparent as this description proceeds.